Electrical transport in porous silicon from improved complex impedance analysis
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Electrical transport in porous silicon from improved complex impedance analysis B. Remaki, S. Perichon, V. Lysenko, and D. Barbier, Laboratoire de Physique de la Matière (UMR CNRS-INSAL 5511), INSA de Lyon, Bat. 502, Avenue A. Einstein, F - 69621 Villeurbanne cedex, France.
ABSTRACT:
An improved analysis of the electrical transport parameters in meso-porous silicon is presented. Our approach is based on a separate contribution of the crystallites and their interconnections to the total impedance of meso-porous silicon layers. Meso-porous silicon morphology exhibits a columnar structure without quantum confinement. The electrical conduction is thus, partially due to the bulk conductivity within continuous paths of crystallites. The samples were realized on -cm p-type Si substrates. Porous silicon layers of 100µm of thickness and 50% of porosity were inserted in Al/SiO2/porous-Si/Si structures. Their electronic transport parameters were determined using complex impedance measurements. A frequency range of 102 - 107 Hz was used allowing an accurate determination of the impedance components. Combined with thermal stimulation, theses measurements provide a powerful tool for the interpretation of basic properties such as the carriers density in the crystallites and the trapping mechanisms. Our results were interpreted in terms of free carriers conduction in partially compensated crystallites prevailing at low frequencies. At high frequencies (above 10 kHz), the electrical conductivity is mainly controlled by hopping transport on localized states in the chaotic porous structure. Finally, the free carriers mobility, evaluated from SCLC measurement is discussed.
1- INTRODUCTION Porous silicon seems to be a promising material with high potentialities in electronics [1,2]. It is obtained from mono-crystalline silicon by electrochemical etching [3]. There are different morphologies depending on the initial type of silicon and the preparation parameters. Nano-porous form (crystallites size around 1 - 3 nm) was widely studied since more than 10 years particularly in the hope of silicon based photo-emitting devices production. Since few years, studies are devoted to other applications [4] such as active layers for chemical sensors, insulating substrates [5 – 7] for thermal microsensors and passive optical devices. Meso-porous silicon is known as an electrical insulator even at low porosity [8,9]. But, the origin of this high resistivity is not well understood until now. Various mechanisms explaining the insulating properties are suggested such as the free carriers trapping by the states of a large specific surface. The experiments based on the frequency dependence and the thermal activation of the conductivity give interesting data on the electrical transport parameters. This approach was efficiently used on nano-porous silicon [10]. In the present work, a similar analysis is applied to the case of meso-porous silicon using an improved implementation of complex impedance measurements.
F3.2.1
2- EXPERIMENTAL Up to 100 µ
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